As is known, optical systems capable of transmitting high amounts of information at a considerable distance with reduced distortion are increasingly employed in the field of communication systems.
Such optical systems employ both optical devices adapted to transmit and/or receive information in the form of light signals, and optical devices such as to allow the propagation of such light signals.
For example, the transmitting/receiving devices include photodetectors, optical signal transmitters, and modulators. On the other hand, the light signal propagation devices comprise, for example, integrated waveguides that are typically called the optical circuits by those skilled in the art.
A method for manufacturing optical devices comprising integrated waveguides on a silicon substrate is described in the document “Glass Waveguides on Silicon for Hybrid Optical Packaging”, by C. H. Henry et al., 7 J. Lightwave Technol., pages 1530-1539, which is included by reference herein below. In particular, the waveguide described in such document comprises a glassy core layer having a respective refractive index. Such core layer is surrounded by glassy coating layers having a refractive index lower than the core layer index. Consequently, a light radiation propagating in the guide remains confined in the core layer.
Furthermore, hybrid optical devices are known, that is, comprising a transmitting and/or receiving optical device associated to the waveguide device. In particular, the latter waveguide device comprises a deviation wall, or turning mirror, which is inclined by a prefixed angle (for example, 45°) relative to a propagation direction of the light radiation in the guide. Such mirror is adapted to deviate such light radiation towards an active portion of the receiving device.
It should be noted that the turning mirrors are manufactured in some waveguide devices by employing metallization layers that are deposited on inclined surfaces opposite the same waveguide, and spaced by trenches from the latter.
In particular, in such devices the light signal must cover a path in the air outside the guide in order to reach the mirror and be reflected towards the receiving device. Consequently, such signal undergoes undesired attenuations and dispersions following the refractive index differential between the waveguide and the air.
U.S. Pat. No. 5,894,538 discloses a method for manufacturing waveguide devices comprising turning mirrors inside the same guide. In particular, such mirrors are obtained by means of a vaporization of portions of the guide coating layers with high-energy light beams. In greater detail, such light beams are incident on the guide coating layers along directions which are inclined relative to the radiation propagation direction, in order to remove portions of such layers in the proximity of a core inlet/outlet end.
It should be noted that in the thus-obtained waveguide devices, the light radiation propagation and reflection take place essentially within the guide coating layers, thereby the light signal attenuations are reduced.
However, in order to manufacture the above-mentioned inner mirrors with an accurate and controllable inclination by conventional techniques, it is necessary to employ advanced and expensive equipments, while performing complex productive process steps.